The use of aryl esters of 3,5-dit-t-butyl-4-hydroxybenzoic acid as light stabilizers for polyolefins, particularly polypropylene, is taught in U.S. Pat. No. 3,112,338. These esters have become increasingly useful as light stabilizers, although processes for their manufacture have not proven to be as commercially attractive as would be desired.
Smutny el al. U.S. Pat. No. 3,112,338, at col, 1, lines 63-71 and in Examples I and II, teach the production of these esters by heating substantially equimolar amounts of 3,5di-tert.butyl-4-hydroxybenzoyl cloride and 2,4-di-tert.butylphenol on a steam bath until molten, resolidifying them and then recrystallizing from Skelly B or ether in 70% yield. This process, due to its low yield, is not suitable for commercial manufacture.
Reaction in a solvent system is also known. Lappin et al., U.S. Pat. No. 3,591,553, teach a process wherein an analogous esterification of 4-hydroxyisophthalic acid with phenols is disclosed. In this process, the acid, an alkylphenol and a condensing agent (phosphoryl chloride, also known as phosphorus oxychloride) are reacted in a hydrocarbon solvent such as toluene, benzene, hexane, heptane etc. However, the reactants (primarily the benzoic acid compound) are not readily soluble in these solvents and productivity using them is poor.
Accordingly, if a process could be found which would enable the production of aryl esters of 3,5-di-t-butyl-4-hydroxybenzoic acid in higher yields and of high quality, a long felt need would be satisfied.